// 2017年12月5日

let Timer = React.createClass({
    getInitialState: function () {
        return { secondsElapsed: 0 };
    },
    tick: function () {
        this.setState({ secondsElapsed: this.state.secondsElapsed + 1 });
    },
    componentDidMount: function () {
        this.interval = setInterval(this.tick, 1000);
    },
    componentWillUnmount: function () {
        clearInterval(this.interval);
    },
    render: function () {
        return (
            <div>Seconds Elapsed: {this.state.secondsElapsed}</div>
        );
    }
});
React.render(<Timer />, document.getElementById("timer"));